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Venomoids - A Practitioner's View
Reproduced with permission of Raymond Hoser
Related to this was the fact that the margin for error in such procedures was not always great and while with experience, losses of snakes under anesthesia are not great, there always remained a risk.
Several veterinary surgeons recommended the use of a modeling clay mould with "arms" to hold down and immobilize sedated reptiles when surgery was to be performed.
In the first instance, a variant of this was planned to perform this operation, but it was ruled inferior to the final means (explained below), as even with clay to restrain a snake, it was possible for a partly sedated snake to be able to squirm it's way out of the holder.
Bearing this in mind, in preparing for the surgery in my case(s) a far more effective means was devised to restrain snakes without incident. This is explained later and shown in the photographs taken at the time and in the absence of other yet unknown better procedures, I strongly recommend that persons doing venomoid surgery use the techniques developed by myself as given in this paper.
The method I devised allowed me to immobilize any species of snake without causing them harm, keep them immobilized as long as necessary and then to allow them to revive almost immediately after surgery. Once a means had been developed to sedate snakes, the only remaining hurdle was the means by which to conduct the surgery.
But before I explain this, I will outline some essential facts about the snake's venom glands.
The venom glands are located above the jawline and generally posterior to the eye to about the back of the skull, usually in the vicinity of and level with the end of the mouth line, or slightly past this and slightly above. This seems to be the positioning in all venomous snakes, including for example the Pacific Rattlesnake (Crotalus viridis oreganus) as shown in Fry 1991 (page 450, top three photos).
The glands (one on each side of the head) are sited under the rear head shields and surrounded by muscle tissue. They sit outside the jawline and with the surrounding muscle tissue form a major part of the flesh in the posterior dorsal head region around the back of the skull. The exact size and positioning of the venom glands varies from snake to snake, but appears to be larger (and reaching further back) in larger snakes of a given species. To the rear, the gland has a rounded end, while anteriorly it narrows to form a vessel or duct that runs under the jaw and into the fang. The length of the venom duct in terms of it's run from the venom gland to the fang tooth also varies from snake to snake. It is not always distinct, in that the narrowing may be fairly rapid, or in some snakes more gradual and this variation appears to even occur within a given species and even with age or size.
In some snakes the duct is up to 1 cm in length and very obvious as a duct, while in some snakes it appears to be almost indistinct with the venom gland almost appearing to narrow and run into the fang.
While more-or-less pointed at one end and with a blunt end at the posterior end, the glands are more-or less rectangular and encased with muscle tissue which appear to help push the venom to the fang. This muscle tissue is fairly easy to separate from the venom glands along the length of the glands, but at the rear, both gland and muscle is affixed to the rear of the head or the flesh of the neck. To separate this, one must cut it. At the anterior end of the gland, the venom duct must also be cut to remove the gland, and when doing so, it is important to cut the duct and not the anterior part of the gland (otherwise leaving part in the snake).
While a number of texts detail the structure of venom glands in snakes, preceding surgery it was essential for me to dissect snakes and look at these structures for myself. Initially it was envisaged that I?d dissect dead captive snakes as "test runs" for surgery", but in late 2003, I was fortunate to find several road-killed Tiger Snakes in order to inspect them.
While some corpses were quite decayed and smelly, they were still adequate for me to inspect the venom glands and test means of conducting surgery, instruments to be used and even refine the means by which I eventually immobilized the snakes in surgery. Tested were both the "external excision" method, by going through the side of the head, and the "internal excision" method, of going through the roof of the mouth, which was ultimately decided to be the preferred method.
It was only after all aspects of surgery had been addressed and tested as best as possible on dead snakes that an operation was conducted on a live snake, which had already been immobilized and kept so for a period equal to or longer than an operation would take and recovered without incident.
THE FIRST VENOMOID OPERATION
The method used for this operation was the same as that used for all others and minor refinements to the means of restraining the reptiles.
The venom glands were removed by an operation into the roof of the mouth to remove them internally, the result being no cutting to the external surfaces or scales of the head.
The subject was a half-grown Tiger Snake. It was placed upside down on a 60 cm long wooden plank (removed from the fridge) and then by it's head and snout sticky taped down to the wood, with the snout and neck at a predetermined spot and held down.
The tape ran over the head only.
The following section of the neck was quickly sticky-taped down to the wood (with the tape running around the board in full circles), with the rest of the snake then being unrestrained but placed over an adjacent towel. The area near the heart (about 1/8 of the way down a snake's total length) was not restrained in any way, (nor was lower down the snake's body in this operation, but for later operations lower down was restrained as well).
The tape over the snake's head and snout was then removed (having been in place for only a few seconds), with the snake itself opening it's mouth to breath. (For those unaware, the glottis, or windpipe of a snake is not always open. It opens and shuts periodically and a momentary blockage is not a fatal condition, so long as it is kept just that, momentary).
The lower jaw and upper jaw were then fixed in a position to allow surgery to start. Veterinary surgeons suggested using string, sutures and other materials to affix the snake's jaws during surgery, but after some previous testing on the snake (without actually doing surgery), it had been established that the best means to affix the jaws and head in place was as follows.
The neck region had already been fixed flat and in a straight line with sticky tape. By it?s nature, this effectively prevented the snake from any means to squirm loose, even if it were to regain consciousness or an ability to move during the operation, which may occur if the snake were insufficiently sedated.
No other effective way was found to properly restrain the snake.
To either side of the head and neck region of the snake and already affixed to the wood plank, were nails. These had been affixed as contact points for so-called "twist ties". These are thin metal strips that can be easily bent and twisted to form a tight line or knot. A long strip was used to affix the lower jaw to the wood, while a second strip was used to do the same to the upper jaw, making sure that the glottis (windpipe) remained clear.
In a breathing snake, this periodically opens and shuts and this remains the case in the snake as it is operated on. A hard-wire frame was set between two nails to hold up the lower jaw (on top) to keep the mouth open for the operation. The nails were set (slightly in facing) to make the frame naturally rise and fix in position, thereby holding the upper jaw in place and fixed.
Nails on the board (several on each side) were spaced apart to allow for any snake to the size of a three-metre elapid and to allow fixing of more than one wire to hold the lower jaw down, so that the fixing wire could be moved if needed if cutting was needed where the wire crossed the snake's mouth.
Due to the lifting of the mouth, twist ties ran through the nails on either side and (after the first operation) on to other nails placed on the sides of the plank (as opposed to the top side where the snake lay). This means that the wire twist ties could be also affixed to these lower nails and hence pull down the mouth (upper jaw on bottom) to be fixed to the board.
Once affixed securely and so that there was no possible movement of the snake, surgery began. For the record, most movement seems to be in the caudal region in the form of undefined coiling and movement.
In terms of the head, the only possible movement is the windpipe opening and closing and the flickering of the tongue, which also gives a good indicator of the level of consciousness of the snake. If one looks, one sees the glottis opening and closing throughout the operation.